Devices peripheral to personal computers are used for a variety of input or output purposes. Computer input devices include keyboards, mice, drawing tablets, cameras, etc., while computer output devices include speakers, printers, monitors, etc. Almost without exception, peripheral devices require a power source for proper operation. Oftentimes the power source comes from a standard cable coupling the peripheral device to the computer, such as connection cables for using Universal Serial Bus (USB, developed by the USB Implementers Forum, Inc.), PS/2 (International Business Machine's Personal System 2), RS232 (now renamed to EIA232 of the Electronic Industries Association), FireWire (Institute of Electrical and Electronics Engineers, Inc.'s 1394–1995 standard), etc. These cables typically provide a 5-volt dc voltage at a given current capacity to drive the device. Computer mice, for example, are typically powered at ˜500 mA, to power the various internal circuits within them that track their movement and communicate the status of their mechanical buttons to their host computer.
Because a mouse cord can be cumbersome and unwieldy, there is a consumer demand for cordless mice. Thus, a new generation of mice have been developed that communicate their signals to their host computer via “wireless” signals, such as infrared (IR), radio frequency (RF), or ultrasonic signals. These wireless mice generally contain their own power source, because including a cord only to supply power to the mouse defeats the purpose of making the signal communication wireless.
The typical solution to self-powering a mouse is to include batteries within the mouse itself. Normally, high-energy batteries such as alkaline batteries are used so that they can provide power for a relatively long time between battery changes. In order to reduce overall power consumption, power saving features are implemented into wireless mice to extend the life of the batteries. For example many wireless mice will automatically “power down” their circuitry after a period of inactivity. Such power savings features can allow wireless mice to operate for months before requiring new batteries.
As new features are added to mice, such as adding a wheel for easy document scrolling, their circuitry becomes more complex. Complex circuitry, in turn, generally requires higher power requirements. These power requirements include not only how much power is needed over time, i.e., how long can a user go before the batteries cannot power any of the mouse circuitry, but also include a peak power requirement, i.e., how much instantaneous power is required to supply a specific circuit in the mouse. Particular circuits such as optical mouse tracking or radio module operations may require relatively high peak energy from the batteries for proper operation.
Although rechargeable batteries generate less power than alkaline batteries, they can be recharged hundreds or thousands of times, and thus provide power at a relatively low lifetime cost. Some computer peripheral products include a “docking cradle” or other place to rest the product during periods of non-operation, and some of the docking cradles include a battery re-charger to automatically recharge batteries in the device while it is in its docking cradle. This is typically done by exposing small electrodes within the docking cradle that transfer power to a matching set of electrodes on the device. Within the device, a circuit transfers the power that is applied to the electrodes directly to the batteries, thereby recharging them.
Requiring a device to be placed in a docking cradle to recharge its batteries means that it cannot be used while recharging. Also, if a user forgets to recharge the batteries for a period of time and they discharge, the user cannot operate the device until the batteries are again recharged. Most likely a user will discover that the batteries are discharged at a time the device is needed. Adding small wires that could recharge the batteries during device operation would defeat the purpose of having a wireless device.
Embodiments of the invention address these and other deficiencies in the prior art.